AC-CDI v2.8

 
On an ACCDI based engine, the charging coil (AKA stator) puts out:
– LV (Low Voltage of around 12Vac) for light and battery if any. (Lighting coil)
– HV (High Voltage of around 100Vac) to charge the ACCDI. (Charging coil)
This AC-CDI only uses the HV coil to charge a capacitor through a rectifier bridge.

When the pickup is triggered, the CDI turns on a thyristor that discharge the capacitor inside the primary of the ignition coil.
This burst of energy into the primary induces a high voltage of few thousand volts into the secondary wiring of the ignition coil, enough voltage to create a spark at the sparkplug contacts.

 

– This CDI works with 1 pickup and 1 reluctor (the metal strip on the flywheel) [A,B].
– This CDI works with 2 pickup and 2 bars [E,F].
– This CDI DOES NOT work with 1 pickup and multi-pulses pickup (ie 2 reluctors on flywheel) [C,D].
– This CDI DOES NOT work with 1 pickup and missing tooth flywheel [G].

– When the engine has only ONE pickup, the 2 wires are connected to HI and GND inputs.
– When the engine has TWO pickups (for Low speed and High speed), the 3 wires are connected to HI, LO and GND inputs.

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Pickup Polarity

– When the rising edge of the bar on the flywheel comes in front of the pickup, a pulse is generated.
This first pulse is used by the CDI to spark at high revs.

– When the falling edge of the bar on the flywheel leaves the pickup, another pulse of opposite polarity is generated.
This second pulse is used by the CDI to spark at idle.

A pickup has 2 wires.
– If you ground wire number 1, wire number 2 will put out a Positive pulse first when the rising edge comes, then a Negative pulse when the falling edge leaves. I call it PN.
– If you ground wire number 2, wire number 1 will put out a Negative pulse first, then a Positive pulse. I call it NP.

A genuine Yamaha pickup is often Positive first then Negative (PN) but if you swap the 2 wires of the pickup, the polarity will be Negative then Positive (NP) therefore the DIP switches setting for PN will NOT work anymore of course !
Solution: Rectify the pickup connection or use the settings for NP engines.

Be careful: If the wires are swapped then the pickup polarity will CHANGE !

To find the polarity connect the pickup to an “old” Analogue meter set to it’s lowest voltage setting (around 1volt).
When a non-magnetized steel object (eg a screwdriver) is approached and comes into contact with the top of the magnet the meter needle will indicate a momentary deflection (ie – negative or + positive volts).
When the screwdriver is removed from the magnet’s top the meter needle will show a brief deflection in the opposite voltage. See: Video

 
Some engines don’t have an external pickup but use only one charging coil to both charge AND to trigger the ignition.
For those engines with charging coils that output 30 to 150volts peak:

Coil is connected between GND and ALT input. (charging)
ALT input is also connected to HI input. (triggering)

Switches N°1, 3, 5 of SW13 are OFF.

Switch N°2 of SW13 is ON to use the Negative wave of the voltage. (timing)
or
Switch N°4 of SW13 is ON to use the Positive wave of the voltage. (timing)

Switches N°3, 4, 5 of SW14 are OFF. [SW14-5 ON may destroy the ACCDI !]

Adjust timing with RV1 [0=Highest advance, 4= Lowest advance]

– Run the bike at idle with RV1 at max value (4)
– Try to rev up the engine while slowly unscrew (toward 0) until the bikes wants to rev up.
– When she wants to rev up you’ve got the setup.

 
You have to know if the bike has 1 or 2 pickups.
Then refer to those lists of settings for bikes with 1pickup or 2pickups
Also you have to know for each pickup what is the polarity:
PN (First pulse Positive then second Negative) or NP (Negative then Positive).

Connect a scope between Ground and pickup wire to check the polarity.
If you don’t have a scope at hand, you can see the polarity with an old voltmeter.

If you still don’t know, you will have to test every possibilities… Follow those guides:

ACCDIv28: Tests all settings for 1 pickup.         ACCDIv28: Tests all settings for 2 pickups.

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DIP SWITCHES

There are 2 banks of switches SW13 and SW14:

SW13 setting

SW14 setting

2 STROKES

SW14-1, SW14-2: Advance timing
4 strokes engines: set Switches N°1 and 2 of SW14 to OFF (default).

On 2 strokes engines it’s necessary to lower the advance at HIGH RPM:
2 strokes with Small reduction of timing : set Switch N°1 of SW14 to ON.
2 strokes with Medium reduction of timing : set Switch N°2 of SW14 to ON.
2 strokes with Large reduction of timing : set Switches N°1 and 2 of SW14 to ON.

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KTM

SW14-3, SW14-4 : KTM setting
All engines, set Switches N°3 and 4 of SW14 to ON (default).
KTM engine, set Switches N°3 and 4 of SW14 to OFF.

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SENSITIVITY

SW14-5: pickup Sensitivity
Pickup that puts out 2 to 30volts, set Switch N°5 of SW14 to ON (default).
Pickup that puts out 30 to 150volts, set Switch N°5 of SW14 to OFF.

Sensitivity Fine tuning

The Sensitivity of the CDI to detect the first pickup pulse (at start and idle) is adjustable with RV2 potentiometer.

– Start the bike with RV2 at max value (4)
– Try different position of RV2 from (4) to (0) to find which position gives the easiest start with no kickbacks.

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SW14-6: Not used
Can be on or off.

 

This CDI doesn’t have seamless advance, it jumps from LOW advance to HIGH advance.
The RPM when the CDI jumps from Low to Full advance (in fact when it switches from the first pickup pulse to the second one) is adjustable with RV1 potentiometer.

– Run the bike at idle with RV1 at max value (4)
– Try to rev up the engine while slowly unscrew (toward 0) until the bikes wants to rev up.
– When she wants to rev up you’ve got the setup.

Example:

2200 rpm with RV1 at 4: CDI uses the second pulse = Low advance

2200 rpm with RV1 at 1.5: CDI uses the first pulse = High advance

 

KILL

A Kill switch input is available at “K” header.
Ignition stops when “K” is connected to GROUND.

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SAFETY

A Safety switch input “S” is available (for Side stand, Clutch, Neutral, Main switches…)
Ignition stops when “S” is connected to a positive voltage from +2v to +12Vdc.

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CHARGING COIL

– If the charging coil is internally grounded, then connect the only wire to “ALT” input and leave “ALTg” not connected. Note that DIP SW13-6 will have no effect.
– If the charging coil is NOT internally grounded, then connect the 2 wires to “ALT” and “ALTg” inputs.
Order has no importance.

SW13-6 DIP ON: Less voltage.
SW13-6 DIP OFF: More voltage (default).

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LED

LEDs have “N” and “P” labels.
They turn on when the CDI receive a Negative or Positive pulse on HI input.

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TACHOMETER

A tacho output “TAC” is available. The output voltage is +12v (even if no battery or 6v battery)
Notice that it’s not a pure square signal.
Connect a tachometer that does NOT need a 50% square signal (50% off, 50% on)

 
You will need a DC voltmeter. The best is an old “Analog Needle meter”.
 

Step 1

Download troubleshoot step1
– Don’t connect any pickup.
– Don’t connect the Kill Switch or any Safety switch.
– Connect the GND plug of the CDI to the ground (minus battery or motorcycle frame)
– Connect the ignition coil to the COIL output of the CDI.
– Remove the sparkplug from the engine head and connect the metal body to a GOOD metal frame (an unpainted bolt).
– Connect a DC voltmeter between GND(ground) and KILL pad.
– If the stator/charging coil IS NOT internally connected to ground, it has 2 wires:
    – Connect one of them to ALT and the other to ALTg input of the CDI.
    – DIP Switch SW13-6 can be ON for full rectification or OFF for half rectification (Don’t hesitate to test both position).

– If the stator (charging coil) IS internally connected to ground, (One wire is already internally connected to ground):
    – Connect the charging coil output wire to ALT input of the CDI.
    – DIP Switch SW13-6 has no effect. (can be on or off).

Other DIP switches positions don’t matter for step 1.
Then:
– Electric start or spin the engine with a drill or Kick start a few times to load the capacitor.
The voltmeter should raise up to 100 or 200Vdc then quickly decrease.
(Due to the capacitor discharging into the CDI and the voltmeter).
If not: Check grounds, connections, joints, charging coil (stator), change switch 6 position.

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Step 2

Download troubleshoot step2
– Same connections as Step 1 (Still no pickup, no kill nor Safety switches connected.)
– Turn SW13 DIP Switches positions 1, 3, 5 to ON.
– Turn RV1 to the minimum resistance (Position: 0).
– Kick start or electric start a few times to load the capacitor.
– Once the main big capacitor C1 is charged and the voltmeter shows 100 to 200Vdc, then in the same second:
– Connect the + 12v battery to HI input:
– Labeled “P” Led turns on.
– The big Capacitor discharge into the ignition coil and one spark must fire at the sparkplug.(plug out of head)
If not: Check grounds, connections, joints, SCR, ignition coil, spark plug cables, spark plug.

Redo this Step 2 but this time connect the +12v battery to the LO input. (Led won’t light.)

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Step 3

Download troubleshoot step3
– Same connections as Step 1 ( Still no pickup, no kill nor Safety switches)
– Turn SW13 DIP Switches positions 2, 3, 4, 5 to ON.
– Turn RV1 to the minimum resistance (Position: 0).
– Connect the pickup coil between a GOOD metal frame (ground) and HI input of the CDI.
– Kick start or electric start to load the capacitor and send trigger pulses:
– The main capacitor C1 is charged and the voltmeter should read 100 to 200Vdc.
– At the same time, when the piston approaches the TDC and passes in front of the pickup, a pulse is produced by the pickup:
– LED blinks. (P or N or both according to the type of pickup)
– The pickup pulse then trigger the SCR and the big capacitor C1 discharges into the ignition coil, a spark must fire at the sparkplug.
If not: Check grounds, connections, joints, pickup coil, RV1 is set at 0?, flip the pickup wires.

 
Analog CDI v2.4 on a XT125/1982:

Pickup polarity (PN or NP):

Analog CDI v2.4 at 15,000rpm:

CDI diagnosis and explanation: